title: Enzymatic biotransformation of the azo dye Sudan Orange G with bacterial CotA-laccase.
abstract: In the present study we show that recombinant bacterial CotA-laccase from Bacillus subtilis is able to decolourise, at alkaline pH and in the absence of redox mediators, a variety of structurally different synthetic dyes. The enzymatic biotransformation of the azo dye Sudan Orange G (SOG) was addressed in more detail following a multidisciplinary approach. Biotransformation proceeds in a broad span of temperatures (30-80 degrees C) and more than 98% of Sudan Orange G is decolourised within 7h by using 1 U mL(-1) of CotA-laccase at 37 degrees C. The bell-shape pH profile of the enzyme with an optimum at 8, is in agreement with the pH dependence of the dye oxidation imposed by its acid-basic behavior as measured by potentiometric and electrochemical experiments. Seven biotransformation products were identified using high-performance liquid chromatography and mass spectrometry and a mechanistic pathway for the azo dye conversion by CotA-laccase is proposed. The enzymatic oxidation of the Sudan Orange G results in the production of oligomers and, possibly polymers, through radical coupling reactions. A bioassay based on inhibitory effects over the growth of Saccharomyces cerevisiae shows that the enzymatic bioremediation process reduces 3-fold the toxicity of Sudan Orange G.
authors.affiliation: Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Av. da República, 2780-157 Oeiras, Portugal.
authors.forename: Luciana
authors.initials: L
authors.lastname: Pereira
authors.forename: Ana V
authors.initials: AV
authors.lastname: Coelho
authors.forename: Cristina A
authors.initials: CA
authors.lastname: Viegas
authors.forename: Margarida M Correia Dos
authors.initials: MM
authors.lastname: Santos
authors.forename: Maria Paula
authors.initials: MP
authors.lastname: Robalo
authors.forename: Lígia O
authors.initials: LO
authors.lastname: Martins
mesh_terms: D001391:Azo Compounds / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology; D001412:Bacillus subtilis / Q000201:enzymology* / Q000235:genetics; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001681:Biological Assay; D001711:Biotransformation; D002851:Chromatography, High Pressure Liquid; D004396:Coloring Agents / Q000378:metabolism; D004563:Electrochemistry; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D042845:Laccase / Q000235:genetics / Q000378:metabolism*; D013058:Mass Spectrometry; D008956:Models, Chemical; D017711:Nonlinear Dynamics; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000254:growth & development; D013053:Spectrophotometry; D013696:Temperature
chemical_list: D001391:Azo Compounds; D001426:Bacterial Proteins; D004396:Coloring Agents; D011994:Recombinant Proteins; C008710:Orange G; D042845:Laccase